Synthesis of cobalt nanodumbbells and their thermal stability under H2, H2/CO and O2 atmospheres

• Co0-hcp nanodumbbells are stable in terms of shape and phase under FTS conditions.
• Reduction-oxidation process led to hollow particles with Co3O4 shell.
• The Co3O4 shell disintegrated to smaller Co0-fcc particles on reduction
• Nanodumbbells are useful to understand the structure sensitivity of cobalt in FTS.

Hexagonal close packed dumbbell-shaped cobalt nanoparticles (Co0-hcp) have been fabricated by the polyol method. The thermal stability of these Co0-hcp nanoparticles has been studied under Fischer-Tropsch Synthesis (FTS) relevant environments such as H2 and H2/CO by using SiO2/SiNx TEM grids which allowed the structural changes of individual particles to be followed after each off line treatment. The TEM analyses demonstrated that the Co0-hcp nanodumbbells are very stable when thermally treated in H2 at 250 °C for 9 h followed by H2/CO at 230 °C, 16 bar for 5 h. These studies indicate that the hcp phase of Co is retained after FTS. Furthermore, subjecting the cobalt nanodumbbells to regeneration conditions such as reduction followed by oxidation led to hollow nanodumbbells with a polycrystalline cobalt oxide (Co3O4) shell (so-called Kirkendall effect) which disintegrated to smaller face centered cubic metallic cobalt (Co0-fcc) particles after further reduction.

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